now, we can call torque a measure of the basic force the engine puts on the crankshaft (and thus the rearwheel through the transmission, countershaft, chain, rear sprocket, etc); horsepower is the overall power resulting from that torque multiplied by engine speed.

longer explanation:

look again at the dyno chart; you'll notice that the torque curve is fairly flat, which means the ninja 250 engine gives a pretty consistent pull regardless of rpm. however, as the revs increase, the hp really starts to build, and the bike accelerates more quickly as the engine approachs redline; the torque is being magnified by the increasing engine speed.

the bike then tugs most smoothly and is most immediately responsive to throttle changes around 9 and 10k, because the torque is more prominent there. but in a 4th gear roll on (which is how such a chart is often obtained), the bike is accelerating it's best around 12 and 13k, because the torque is getting used more often at higher revs, making it more useful.

so, now you might understand while a vehicle with a lot of torque (like a v-twin) is great for around town, where throttle changes are frequent (and shifting can be tiresome), while a vehicle with a lot of high-end hp (like an inline-four) is great for the open road when you can rev the engine freely and time your shift points how you please. the ex250 is a nice compromise for hp and torque.